Many wireless devices communicate with each other using a set of one or more radio spectrum bands that have been statically allocated for their use. These devices may be referred to as the primary incumbents (or primary users) of the spectrum that they use. For example, cellular telephones are primary incumbents of the spectrum licensed by their cellular operator, and no other device is permitted to use this spectrum for communication unless it is registered with the corresponding cellular operator. Further, while specific spectrum bands are allocated for use by their primary incumbents, the primary incumbents are not free to use their allocated bands to operate any type of air interface. For example, a television service provider cannot independently decide to begin operating a cellular service on spectrum bands allocated for its use.
The Federal Communications Commission (FCC) has estimated that over 70% of the allocated spectrum is not being used by its primary incumbents at any given time, even in crowded areas where usage is intensive. Accordingly, the radio spectrum is being severely underutilized.